It is known to use non-contact gages to measure critical dimensions of precision workpieces after intermediate or final machining steps have been accomplished. Measuring the workpieces is desirable to monitor the quality of the workpieces being produced, and also can provide information that may be used to extend the service life of the machining tools being employed.
One type of non-contact gaging device comprises a small-diameter nozzle positioned in close proximity to the workpiece surface to be measured. Compressed air is supplied to the nozzle and the escape of pressure from the nozzle is throttled by the workpiece. By measuring the back-pressure at the nozzle it is possible to determine with a high degree of accuracy the distance between the workpiece surface and the nozzle. One of the advantages of such a pneumatic gage is that a continuous stream of measurements may be taken as the gage moves relative to the workpiece.
U.S. Pat. No. 5,152,166 discloses a pneumatic measuring device wherein the gage is mounted on a rotating shaft which is inserted into a bore after the forming tool has been withdrawn therefrom. The nozzle of the gage is directed radially outward so that it describes a spiral pattern over the inner surface of the bore as the rotating shaft is advanced into the bore. The pneumatic gage can not be inserted into the bore until after the tool which formed the bore has been withdrawn.
U.S. Pat. No. 3,059,381 discloses an apparatus for honing the interior surface of a machined bore and having a pneumatic gaging device for monitoring the diameter of the bore. The gaging device is mounted at the end of an arm which extends adjacent the outer surface of a rotating shaft to which honing stones are fixed. During operation of the machine, the rotating shaft is repeatedly inserted into and withdrawn from the bore, the honing stones gradually increasing the internal diameter of the bore with each stroke. The arm carrying the pneumatic gage is also inserted into the bore with each stroke of the shaft so that the gage is brought into close proximity to the inner surface of the bore at one point on its circumference and takes a measurement of the bore diameter at that point. When the gage senses the desired finished diameter, the machine automatically terminates the honing process.